Fluid pressure control device



Aug. 4, 1942.

J. A. MULLER FLUID PRESSURE CONTROL DEVICE -2 Sheets-Sheet 1 Filed Sept. 9, 1958 SMM fw Aug- 4, 1942. J. A. MULLER lFLUID PRESSURE CONTROL DEVICE 2 Sheets-Sheetl 2 File@ sept. 9. 1938 Q of;

a ,d w, L a j n A Hman A. Muller.

Panarea Aug. 4, 1942 FLUID PRESSURE CONTROL DEVICE Johan A. Muller, Mount Gilead, h10, assigner to The Hydraulic Development Corp. Inc., Wilmington, Del.. a corporation of Delaware Alpllclfloll September 9, 1938, Sel'lll N0. 2 29,21

(ci. sei-sz) g one ci which is connected to the fluid discharge 4Clalms.

This invention relates to hydraulic machinery, and in particular to hydraulic 'devices and cir#- cuits for accurately controlling the pressures applied to workpieces by hydraulic machinery.

One object oi' this invention is to provide a hydraulic device 'and circuit for accurately controlling the maximum pressure applied to a hydraulic machine, such as a press, especially such a machine wherein the ram moves rapidly and comes to an abrupt stop.

Another object is to provide a hydraulic con:- trol device which, immediately upon the attainment of a predetermined pressure in the machine circuit, will automatically by-pass the pressure iluid discharged from the pump and at the same time set in operation the control `mechanism which reverses the pump discharge, thereby eliminating the time lag previously occurring between the arising oi the predetermined pressure and ythe operation of the pump control mechanism.

Another object is to provide a hydraulic control device which simultaneously by-passes the pump discharge and operates a limit switch for actuating the pump reversing circuit in response to the attainment oi a predetermined pressure in the circuit to'which the device is connected.

Another object is to provide a hydraulic press circuit including a pressing plunger, a reversible variable delivery pump and a hydraulic control device, interconnected by electrical and hydraulic circuits of such a nature that the control device automatically by-passes the pressure fluid discharged by the pump and at the same time efiects the actuation of the pump reversing mechanism at the instant that a predetermined pressure arises in the circuit by reason of the action oi the pressing plunger upon the work or devices being pressed by the press.

In the drawings:

Figure l is a central longitudinal section through the hydraulic control device of this in vention, with the parts thereof in position prior to the attainment of the predetermined pressure.

Figure 2 is an enlarged sectional view of the lower portion oi Figure '1, showing the parts shifted to by-pa-ss the pump discharge and operate a limit switch in response to the attainment of a predetermined pressure.

Figure 3 is an enlarged sectional view of the upper portion of Figure 1.

Figure 4 is a diagrammatic view oi a simplied circuit utilizing the hydraulic control device oi this invention.

General arrangement In general, the hydraulic control device of this invention consists of a spring-pressed valve plunger, which likewise rcarries a switch-operating cam. The valve plunger in one position cuts oil intercommunication between two chambers,

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line, such as to the iluid tank, whereas the other is connected to the pressure circuit, such as tothe main cylinder-'of a hydraulic press. At a predetermined pressure the valve plunger overcomes the thrust oi' a spring and automatically shifts to by-pass the pressure circuit by opening communication between these two chambers. The valve plunger also carries a cam which actuates a limit switch at the instant the predetermined pressure is reached and the plunger is shifted, this limit switch controlling an electrical circuit which sets in motion the reversing mechanism oi the reversible variable delivery pump used to supply iluid to the circuit and press.

Hitherto, one oi' the serious problems encountered by hydraulic engineers has been to accurately control the maximum pressure applied to or by a press, particularly where the pressing plunger moves rapidly and vthen comes to an abrupt halt. In many pressing operations the pressing'plunger, under modern pressing conditions, is required to move at a comparatively rapid rate to insure emcient and economical production, yet at the end of this motion it engages a workpiece which yields but slightly. The-presssure exerted by or against the pressing plunger shall reach a certain limiting pressure, and not exceed this pressure. For example, in coining operations the pressure must reach a certain value in order to satisfactorily form'the details of the workpiece, yet must not exceed that pressure or the workpiece will be damaged.

Under previous arrangements for controlling this pressure, the pump control mechanism has been set so that it will be actuated when this maximum pressure is reached. In practice, however, a time lag occurs during which the pressure rises above the desired maximum pressure while the pump control is shifting to reduce the discharge of the pump. Setting the pump control to operate at a lower pressure to make an allowance for this overrun oi pressure, gives no definite assurance that the required pressure will be reached, and the workpiece may therefore be nsuiliciently pressed.

Hydraulic control device i5. Passing Y Beyond a reduced diameter portion I1, Reciproca-ble within the valve bore I4 is a valve plunger. generally designated I8, and having a large diameter portion I9 and a small diameter portion 20 interconnected by a reduced diameter neck 2l. Beneath the reduced diameter portion 210' the valve plunger I8 is provided with a stem 22, terminating in a reduced diameter threaded portion 23, carrying a threaded nut or collar 24, an internally threaded cam 25 in the-form-of a hollow collar, and a locknut 26 for locking the cam 25 in any desired position. The cam 25 is provided With an internal bore 21, which extends over the outer surface of the nut or collar 2li.

Attached to the valve casing Iii at its lower end is a switch casing 28, carrying a normally closed pressure-responsive limit switch 291 having an operating member 39. A cover 3l at the end of the switch casing 28 gives access to the limit switch 29 and cam 25. Likewise secured to the valve casing I as by the screws 32 and. within the limit switch casing 28 is an oil seal retainer 33, in the form of a collar surrounding the valve stem 22 and having anaxial extension 311i serving as a spacer to limit the motion of the valve plunger I8. The threaded nut or collar 25 cooperates for this purpose with the spacer portion 34. Within the oil seal retainer 33 is an oil seal 35 surrounding the valve stem 22 to prevent leakage therealong. The valve plunger it is provided with a longitudinal bore 36, communicating with a cross bore 31 for draining leakage fluid from the leakage chamber 39 adjacent the oil seal 35. The chambers II and l2 are provided with threaded ports 39 and 40, serving respectively as inlet and outlet ports for the connection of the pressure and discharge conduits.

The upper end of the valve plunger I8, after passing through the -bore portion I5, terminates in an enlargement or flanged cap 4I for receiving the thrust of one end of ,la coil spring 42. 'I'he coil spring 42 is mounted within a tubular `spring casing 43, secured tothe valve casing I0 sions.

different diameters, this dilerence providing a differential plunger area which makes it possi-ble to keep the spring 42 down to reasonable dimen- By making the portion I9 of but slightly greater diameter than the portion 2i), a comparatively small spring 42 may be used because it is on the area which represents the diiierence l`netween these two diameters that the fluid presy sure acts.

In the operation of the pressure control device of this invention the connection port 39 of the vvalve casing l0 is connected to the pressure through the chamber II and out through the by means of the bolts 44 and annular flange 45,

- a gasket 46 preventing leakage. The flange 45 is secured, as by welding, to the casing 43. The upper end of the spring casing 43 is similarly connected by similarly designated Darts to the spring adjusting casing end plate 41. The latter 'is provided with a bore 48, within which is mounted an internally threaded collar or nut 49, as -by the screws 50. The threads of the collar 49 receive a threaded adjusting steml, having an internal bore 52 for receiving the upper portion 153 of the upper spring cap 54, which receives the thrust of the upper end of the coil spring 42. A ball thrust bearing 55 is arranged between the spring cap 54 and the end of the threaded adjusting stem 5I. Surrounding the latter is a spring adjusting casing 56, which .with the end plates 41 and 51 forms a slippage chamber for receiving fluid which leaks into the space surrounding the stem 5I. The spring casing 43 and the spring adjusting casing 56 are provided with threaded ports 58 and 59, to which are connected respectively the leakage conduits 60 and 6I, which serve for draining oil the leakage liuid.

The stem 5I terminates in an unthreaded portion 62,.surmounted by a hand wheel 63, leakage being prevented by a packing 64 and gland 65, through which pass the threaded studs 66 engaged by the' adjusting nuts 61. The spring adjusting casing 56 provides an oil-tight, dustproof Aprotection for the threads of the threaded stem 5I. The threaded nut or collar 49' is in port 49 to the discharge circuit. This instantly lay-passes or unloads the discharge of the pump, thereby preventing the pressure in the circuit from going higher than the predetermined maximum pressure. At the same time the motion of the valve plunger I8 causes the cam 25 to engage' and trip the switch member 30 of the normally closed limit switch 29, thereby opening the limit switch l29 and controlling an electrical circuit,which in turn,'controls the pump discharge. The reduced diameter neck 2l between tlie valve portions I9 and 20 enables the flow of fluid to be materially increased. Since the cam 25 is adjustable independently ofthe coil spring 42, the action of the limit. switch 29 Ican be advanced or delayed as required by the particular operating conditions.

,By this invention, therefore, the entire discharge of the pump is by-passed when the desired pressure is reached and the press, or other machine which is controlled, cannot be subjected to more pressure than that for which the conf trol device is set. Any leakage which occurs passes through the cross bore 31 and longitudinal bore 36, into the spring casing 43, whence it is drained oil` through the port 58 and drainage line 63.

Pressure-controlled hydraulic pressing circuit In Figure 4 is shown a simplied pressing circuit including the control device, previously described and generally designated 1I). Also included inthe circuit is a hydraulic press, generally designated 1I, a reversible variable delivery pump, generally designated 12, and shuttle valve, generally designated 13, a contactor switch, generally designated 14, a. solenoid 15 for operating the pump control, and a manual switch 16'. for initiatingl the operation of the circuit.

the amature 84 of the solenoid 15. The details of the pump 12, thel servomotor 11 and the safety centering device 18 form no part of the present invention and are disclosed in the copending Ernst application, Ser. No. 170,250, iiled October 21, 1937, now Patent No. 2,184,665.

Associated with the pump 12 is a tank 85 for containing the working fluid, such as oil. 'I'he pump 12 is connected by the conduit 86 to one end of the shuttle valve 13, the other end of which is connected by the conduit 81 to the conduit 88 leading to the upper port 89 of the main Vcylinder 90. The latter is provided with a main lunger 9| having a piston head 92 and a lower port 93, to which is connected the conduit 94 running back to the same pump connection 95, to which the conduit 86 is connected. The opposite pump connection 96 is connected by the 'conduit 91 to the conduit 88. The shuttle valve f 13 is of a conventional type, having a shuttle valve member 98 reciprocable in the ports 99 and |80 of the partitions |0| and |02. The pipe |03 serves to discharge into the tank 85. i

The shuttle valve member 98 is provided at its ends with enlarged heads |04 and |05, respectively. The conduit 88 is connected at its lower end to the inletA port 39 oi the pressure control device 10, the outlet port 40 being connected by the conduit |06 to the tank 85. The conduit 60 is also connected to the conduit |05. The press 1| is provided with strain rods |01 interconnecting the main cylinder 90 with the press bed |08, upon which the workpiece is mounted together with suitabledies, molds or other apparatus depending upon the pressing conditions. The shuttle valve 13 is shown for purposes of simplifying the circuit in order to avoid the lengthy description required when a surge valve and main cylinder relief and by-pass valve are alternatively used in connection with the main cylinder 90.

. The shuttle valve 13 merely serves in a well known manner to compensate for thediiference in fluid required by or discharged from the opposite ends of the main cylinder 90, due to the volume occupied by the main plunger 9|.

In the operation of the circuit shown in Figure 4, it is assumed that the main plunger 9| occupies the retracted position shown. To start the main plunger 9| downward to initiate a pressing stroke, the operator closes the manual switch 16. This closes the circuit from the electrical supply lines |09 and ||0, through the normally closed pressure-responsive limit switch 29 and the winding of the conductor 14, closing the switch blades nH2, ||3 and ||4 thereof. The switch blade I4 operates a holding circuit which maintains the energization of the contactor winding III when the manual switch 18 is released. 'I'he closing of the contacter switch blades ||2 and |13 upon their contacts energizes the solenoid and causes the armature 8| thereof to be drawn downwardly. This action shifts the bellcrank 83 and consequently the servomotor valve rod 19, causing the servomotor 11 to pull the flow-control element or shiftring of the pump 12 to a position causing the pump to discharge pressure fluid through the conduits 91 and 88 and the port 89, into the upper end of the main cylinder 90, above the main plunger 9|. At the same time the pressure passing through the branch conduit 81 acts against the shuttle valve head |04 and shifts the shuttle valve member 98 to the right, closing the left-hand end chamber thereof and openlng the right-hand end chamber to communicanon with the tank as through the pipe m. The pump then draws in fluid through the conduit 86 and shuttle valve 13, and discharges it through the conduits 91 and 8B.

The main plunger 9| movesdownwardly until built'up within the main cylinder 9|, this pressure being transmitted back through the conduit 88 and port 39 in the valve casing ll0 of the pressure control device 1l. When the pressure rises t0 the predetermined maximum for which the device 10 is set, the valve plunger I8 moves upwardly in the manner previously described, permitiing the pressure uuid to be discharged through the valve chambers I2 and Il and the port 40, into the discharge conduit |08 leading back tothe tank I5.

At the same time the cam 25 on the valve stem 22 engages the limit switch member 3l and opens the normally closed pressure-responsive limit switch 29. This action deenergizes'the circuit between the lines l|5 and Ill, deenergizing the winding of the contacter 14, opening the latter Aand deenergizing the solenoid 15 through its lines ||1 and H8. The deenergization of the solenoid 15 permits a spring within the servomotor 11 to shift the valve rod 19 thereof in such a manner as to operate the servomotor and shifts the flow-control member or shift-ring of the pump 12 through its neutral position, into its reverse position. This reverses the discharge of the pump 12 and causes pressure fluid to be subsequently discharged through the conduit 94 and port 93, into the lower end of the main cylinder 90. At the same time, fluid is withdrawn through the port 89 and conduit 88 from the upper end of the main cylinder 90, and the shuttle valve member 98 shifts to the left into the position shown in Figure 4. This allows the fluid, which is pushed out of the main cylinder 90 by the rising plunger 9|, to escape into the tank 85. This uid is in excess of that handled by the pump 12 and forced by the latter into the lower port 93 of the main cylinder 90 to retract the main plunger 9|.

As soon as the pressure drops in the conduit 88, the valve plunger I8 will be forced downwardly by the coil spring 42 within the pressure control device 10, releasing the switch-operating member 30 and causing the limit switch 29 to close. Since the winding III of the contactor 14 has been deenergized, however, nothing more will happen until the operator again closes the switch 16. In this manner it will be seen that the discharge of the pump 12 is by-passed by the iiuid pressure control device 19 the veryvinstant the main plunger 9| encounters a pressing resistance above the predetermined desired amount. This by-passing or unloading of the pump discharge relieves the pressure during the time lag period in which the pump servomotor 11 is reversing the delivery of the pump 12.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims.

Having thus fully described my invention, what' I claim as new and desire to secure by Letters Patent, is:

Y 1. In a hydraulic press circuit, a reversible variable delivery pump .having a pump flowcontrol element connected thereto, a main cylinder, a pressing plunger therein, a hydraulic iable delivery pump having apump flow-control element connected thereto, a main cylinder, a pressing plunger therein, a hydraulic circuit interconnecting said main cylinder and said pump, and means responsive to the attainment of a predetermined pressure in said circuit for shifting the flow-control element of said pump from a forward delivery position to a reversed delivery position and substantially simultaneously unloading the full discharge of said pump while said flow-control element is-still in a forvvard delivery position.

3. In a hydraulic pressA circuit, a reversible variable delivery pump having a pump flow-control element connected thereto, a main cylinder, a pressing plunger therein, a hydraulic circuit interconnecting said main cylinder and said pump, electrical means for shifting said flowcontrol element. and means responsive to the attainment of a predetermined pressure in said circuit for altering the energization of said electric means to shift said now-control element through a zero delivery position and for substantially simultaneously unloading the discharge of said pump before said flow-control element reaches said zero delivery position during said shifting operation.

4. In a hydraulic press circuit, a main cylinder, a pressing 'plunger reciprocable therein, a. reversible variable delivery pump connected to said cylinder and having a reversible pump flowcontrol member associated therewith for reversing the discharge of fluid from said pump to said cylinder for advancing and retracting said pressing plunger, and meansresponsive to the attainment of a predetermined pressure in said main cylinder for reversing the pump flow and for substantially simultaneously unloading the full discharge of said pump while said reversible flow-control member is being moved to its reversed position.

JOHAN A. MULLER. 

